(a) Field of the Invention
The present invention relates to a communication method. More particularly, the present invention relates to a transmission timing of a packet or message.
(b) Description of the Related Art
A duplex communication scheme used in a wireless mobile communication system may be classified into a Frequency Division Duplexing (FDD) transmission mode scheme for uplink (UL) and downlink (DL) bidirectional communication which distinguishes uplink and downlink transmission and reception resources based on frequency and a Time Division Duplexing (TDD) transmission mode scheme for uplink and downlink bidirectional communication which distinguishes uplink and downlink transmission and reception resources based on time.
A wireless mobile communication system generally employs a communication frame to perform communication.
Next, a communication frame will be described with reference to FIGS. 1 and 2.
FIG. 1 illustrates a communication frame of a Frequency Division Duplex (FDD) scheme in the conventional art.
As illustrated in FIG. 1, a communication frame of a Frequency Division Duplex scheme frequency scheme comprises F downlink subframes and F uplink subframes. F corresponds to the number of subframes.
Downlink subframe indices 0 to F−1 are assigned to the F downlink subframes, and uplink subframe indices 0 to F−1 are assigned to the F uplink subframes.
FIG. 2 illustrates a communication frame of a Time Division Duplex (TDD) scheme in the conventional art.
As illustrated in FIG. 2, a communication frame of a Time Division Duplex scheme frequency scheme comprises D downlink subframes and U uplink subframes.
Downlink subframe indices 0 to D−1 are assigned to the D downlink subframes, and uplink subframe indices 0 to U−1 are assigned to the U uplink subframes.
To achieve high speed data packet transmission, low delay, and transmission reliability, mobile communication systems are making use of a Hybrid Automatic Repeat Request (HARQ) scheme which incorporates a Forward Error Correction (FEC) scheme and an Automatic Repeat Request (ARQ) scheme.
In the ARQ scheme, an error is corrected through data packet retransmission, for which a stop and wait (SAW) scheme, a go-back-N (GBN) scheme, a selective repeat (SR) scheme, and the like, are used. The SAW scheme is a scheme in which whether or not a transmitted frame has been properly received is first checked and a next frame is then transmitted.
According to the HARQ scheme, a receiver checks whether an error occurs by decoding a data packet received by a physical. If no error occurs, the receiver transmits an acknowledgement (ACK) signal as a response signal to inform a transmitter about the successful reception of the data packet. If an error is detected from the received data packet, the receiver transmits a negative-acknowledgement (NACK) signal as a response signal to inform the transmitter about the error detection. Upon receiving the NACK signal, the transmitter may retransmit data.
The retransmission scheme of the HARQ may be classified into a synchronous HARQ scheme and an asynchronous HARQ scheme depending on the transmission timing of a retransmission packet. In the synchronous HARQ scheme, the transmission timing of a retransmission packet for an initial transmission packet is kept constant. In the asynchronous HARQ scheme, a scheduler of a base station determines the transmission timing of a retransmission packet for an initial transmission packet.
The HARQ may be classified into an adaptive HARQ and a non-adaptive HARQ according to whether the amount and positions of allocated resources are varied. The adaptive HARQ is a scheme in which the amount and positions of allocated resources are varied. The non-adaptive HARQ is a scheme in which the amount and positions of allocated resources are fixed.
By properly combining the synchronous and asynchronous HARQ schemes and the adaptive and non-adaptive HARQ schemes together, and employing low signaling overhead, a high scheduling gain and a high-speed data transmission effect are achieved. For example, a mobile communication system may adopt an adaptive asynchronous HARQ for downlink data transmission and the synchronous HARQ for uplink data transmission.
To reduce signaling overhead caused by a control signal, such as resource allocation information, it may be effective to use a synchronous, non-adaptive HARQ scheme in which a retransmission timing and the amount and positions of allocated resources are not varied. But, it is rather effective to use an asynchronous, adaptive HARQ scheme with a scheduling gain without consideration for signaling overhead.
By properly combining the synchronous and asynchronous HARQ schemes and the adaptive and non-adaptive HARQ schemes together, and employing low signaling overhead, a high scheduling gain and a high-speed data transmission effect are achieved.
If a terminal uses the synchronous HARQ scheme for downlink, the terminal needs to be allocated resources from a base station through a downlink control signal in order to transmit a HARQ packet on an uplink. That is, uplink transmission resources are allocated through a downlink control signal, and a HARQ packet is transmitted in a designated position (slot or subframe). Moreover, if the HARQ packet is successfully received without an error, the base station transmits an ACK as an HARQ feedback signal. On the contrary, if the reception fails, the base station transmits an NACK. Upon receiving the NACK as the HARQ feedback signal, the terminal retransmits the previously transmitted packet.
Particularly, in a TDD transmission mode which distinguishes uplink and downlink transmission and reception methods, a gain can be obtained more efficiently by taking into account efficient timings of time division transmission and resource allocation using the ratio of uplink and downlink frequencies and the ratio of uplink and downlink transmission channels.
In the TDD transmission mode, one frame may consist of one or more subframes for DL and UL. The ratio of subframes allocated for DL and UL may be varied according to the pattern of a frame structure. If the number of subframes constituting one frame is 6, 7, or 8, one of various frames structures, including 3:3, 4:2, 2:4, 5:2, 3:4, 4:3, 2:5, 6:2, 5:3, 4:4, 3:5, 2:6, . . . may be selected.
A wireless mobile communication system may use a Transmission Time Interval TTI as a transmission time unit. TTI is the duration of the transmission of the physical layer encoded packet over the radio air interface, and is equal to an integer number of Advanced Air Interface (AAI) subframes. That is, 1 TTI is the duration of transmission of a packet (subpacket or data burst) occupying a length of 1 subframe, and n TTI is the duration of transmission of a packet occupying a length of n subframes.
Moreover, a data burst may be transmitted over one subframe, or may be transmitted over a plurality of consecutive subframes. For transmission of a data burst in one frame, the duration of the data burst is referred to as one TTI or a default TTI, whereas, for transmission of a data burst over a plurality of consecutive subframes, the duration of the corresponding data burst is a Long TTI. For example, for Long TTI transmission in the FDD transmission mode, a data burst may be defined to occupy a length of four subframes, whereas, for Long TTI transmission in the TDD mode, a data burst may be defined to occupy the entire DL or UL subframes in one frame for DL or UL.
In some systems, the length of subframes occupied by the data burst that are transmitted in accordance with a required packet size may be differently determined as 1 TTI, 2 TTI, 3 TTI, . . . depending on the characteristics of the data.
According to the conventional synchronous HARQ method, the transmission of a control signal for resource allocation, an HARQ packet, and a corresponding HARQ feedback signal are adapted to occur at a predefined timing. Particularly, for uplink UL, an HARQ packet is retransmitted in the same subframe position as the preceding subframe in which the data burst has been transmitted.
According to the conventional synchronous HARQ method, in the TDD mode, an HARQ transmission and reception procedure of DL and UL data bursts allocated to a subframe adjacent to DL and UL switching points may bring about the following problems.
That is, no consideration is being given for variations of an HARQ reference timing with data burst processing time and control signal processing time that may be varied or fixed in accordance with the packet processing capability of a base station and a plurality of terminals. Moreover, processing capability and processing time are not flexible since transmission occupation time for data bursts of various lengths is not taken into account. In addition, one way access delay for DL and UL may occur because packet transmission and feedback signal transmission may be delayed or slow. For this reason, high-speed packet transmission is not possible, and the delay of the HARQ procedure may lengthen the buffer's waiting time in operation and make an HARQ timing procedure complicated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.